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Firefighters have increased containment of California's Rim Fire to 60 percent, even as the blaze has continued to spread to 348 square miles, officials reported on Monday morning.

(Photo: Flickr / California National Guard)Yosemite's Rim Fire has grown to 348 square miles, making it the fourth largest in California history.

Five thousand firefighters from around the state, up more than 1,000 in the past week, in combination with lighter winds, higher humidity and a brief rain shower on Saturday night, have helped combat the flames, though winds have not died out completely and at times instigated spot fires.

U.S. Forest Service spokesman Trevor Augustino told The Los Angeles Times that while the current weather had enabled firefighters to clear brush, set backfires and bolster containment lines, "any rain we get would be a tremendous asset."

The Rim Fire, the largest fire recorded in Sierra Nevada history and fourth largest in California state history, has currently burned almost 225,000 acres according to Cal Fire. It is also reporting that the fire has obliterated 100 structures, 11 of which are homes, though it currently threatens 5,506 structures, the majority of which are residences.

While the Hetchy Hetchy Reservoir, the dam containing San Francisco's primary water supply, has been threatened by the fire, so far the water quality has remained untainted since the start of the fire, says the San Francisco Public Utilities Commission.

While many tourists have stayed away from Yosemite, the park is still open for visitors although the fire has closed some park roads, and recent winds have pushed smoke into the park, prompting smoke advisories, warnings guests against overly strenuous activity.

The Rim Fire has already cost California and the federal government $60 million in government funds, said Augustino. This is on top of the funds that are also being used to fight the six other fires currently burning within the state. Augustino credited the hot weather, winds and dry lightning with igniting the other blazes.

Officials are still determining the cause of the Rim Fire. In a community meeting on August 23, Todd McNeal, the fire chief in Twain Harte, a small town outside of Yosemite, explained that he believed the fire was started by an illegal marijuana farm.

"We know it's human caused, there's no lightning in the area," he said. "[We] highly suspect that it might be some sort of illicit grove, marijuana grow-type thing."

Others have blamed tree thinning projects that the U.S. Forest Service has approved but were never funded by Congress, saying that the plethora of tinder made it all too easy for a fire to grow to this size.

"We know the last fire in that area was in about 1905. That's 100 years without fire," UC Berkeley Researcher Scott Stevens told The San Francisco Chronicle. "If you don't clear trees and brush and do some prescribed burning, you are eventually going to get a very closed forest that is very dense."